Lately I attended Startup Weekend Singapore. One of the event sponsors was Evernote, who kindly gave out free 3-month subscriptions for Evernote Premium to all participants. Coupon looked like this:

Notice that 20-char code? Have fun keying it in a web form!
Meanwhile, our old friend QR code, generally abandoned and misused, could have been a perfect candidate for the job.

Just a little modification of Evernote’s, already powerful, mobile app is needed to recognise QR code and apply discount to user’s account. Existing customers could have enjoyed convenience, while those without an app, will be incentivized to download it.